1. Field of the Invention
The present invention relates to an apparatus and method for performing a handover in a mobile communication system, and more particularly to an apparatus and method for performing a handover between first and second mobile communication networks according to a movement of a user who uses a mobile communication terminal for supporting both first and second mobile communication services to establish a call connection state.
2. Description of the Related Art
Mobile communication service systems may be classified into synchronous mobile communication systems and asynchronous mobile communication systems. Typically, asynchronous mobile communication systems are classified into WCDMA (Wideband Code Division Multiple Access) systems and UMTS (Universal Mobile Telecommunications System) which has been adopted as European Standard (ES). Synchronous mobile communication systems are adapted to accurately establish synchronization with all base stations because they employ GPS satellites. For example, two kinds of synchronous mobile communication systems, are second-generation CDMA systems such as IS-95 or J-STD008, which are serviced in Korea and the USA, and CDMA2000, which has been adopted as American National Standard.
WCDMA asynchronous mobile communication service standardization is in progress in the 3GPP (3rd Generation Partnership Project). WCDMA is based on the European Standard GSM. CDMA-1X synchronous mobile communication service standardization is in progress in the 3GPP2. CDMA-1x is an upgrade from IS-95B. Therefore, compatibility between WCDMA and GSM is being fully investigated in the 3GPP, and compatibility between the CDMA-1X and IS-95A/B has already been implemented.
Though construction of the WCDMA network is progressing with a large area of interface with CDMA-1X, it remains impossible to perform a handover when a call connection state moves from the WCDMA network to the CDMA-1X network because there is no communication standard in common between WCDMA and CDMA-1X. In other words, it is impossible to perform a handover because procedures for interworking between independent communication systems (i.e., a synchronous system and an asynchronous system) are not defined.
A mobile communication terminal connected to a synchronous communication network and serviced thereby should continuously receive a synchronous mobile communication service. Similarly, a mobile communication terminal connected to an asynchronous communication network and serviced thereby should continuously receive an asynchronous mobile communication service.
In conclusion, it is necessary for a mobile communication terminal to perform handovers from a synchronous network to an asynchronous network or from an asynchronous network to a synchronous network according to movement of the terminal, but prior art mobile communication terminals have no apparatus or method for performing such handovers.
Therefore, when a user in a call connection state via an asynchronous mobile communication network moves to an area of a synchronous mobile communication network, the call connection state is interrupted. For example, if an asynchronous mobile communication network is installed in a narrow area such as a city, and a user in a call connection state within the city moves to areas without an asynchronous mobile communication network, the call connection state is interrupted.
In light of the development of asynchronous mobile communication service, it is anticipated that such a service will be initially provided only in a prescribed area, and will then be provided throughout a whole country. Considering this fact, a method of enabling handovers between different mobile communication networks is needed.